1. Field of the Invention
The present invention relates to a cutter machine, which is used in a pelletizer or the like.
2. Description of the Related Art
FIG. 10 shows the structure of a conventional pelletizer for plastic material. In order to obtain a satisfactory pellet by cutting molten plastic material extruded from a die plate 101, the cutting surface 104 of knives 103 and a resin-discharge surface 102 in the die plate have to be always maintained parallel to each other during the operation of the pelletizer. Consequently, it is necessary to precisely adjust the perpendicularity between the cutter shaft 106 onto which a knife holder 105 (onto which the knives 103 are mounted) is mounted and the resin-discharge surface 102 in the die plate prior to the operation.
However, in the pelletizer shown in FIG. 10, the connection between the knife holder 105 and the cutter shaft 106 is fixed. As a result, a deviation in the pre-adjusted perpendicularity between the cutter shaft 106 and the resin-discharge surface 102 in the die plate due to a small thermal stress and others in various portions of the pelletizer causes the parallelism between the cutting surface 104 of the knives 103 and the resin-discharge surface 102 in the die plate to be deviated and thereby to provide an incomplete cutting.
In conventional knife holders shown in FIGS. 11 and 12, it is intended that the parallelism between the resin-discharge surface 102 in the die plate and the cutting surface 104 of the knives 103 is always maintained by the resilience of a gum bush 110 or a metal plate 111, which are disposed inside the knife holder 105, even if the perpendicularity is deviated during the operation.
In this case, the knives 103 are rotated by a drive apparatus 109 in the state in which the knives are always pressed against the resin-discharge surface 102 in the die plate via the cutter shaft 106 by means of a press apparatus (not shown). When the parallelism between the cutter shaft 106 and the resin-discharge surface 102 in the die plate is deviated, a space takes place in part of the circumferential contact area between the knife 103 and the resin-discharge surface 102 in the die plate. Since, however, the knives 103 are pressed against the resin-discharge surface via the cutter shaft 106 and the knife holder 105, a deformation either in the gum bush 110 or in the metal plate 111 disposed inside the knife holder 105 causes the knives 103 to be pressed against the resin-discharge surface 102 in the die plate and therefore to be in contact therewith over the entire circumferential contact areas, thereby enabling a satisfactory cutting to be obtained.
In the conventional knife holder, a spring action effect obtainable either from the gum bush in FIG. 11 or from the metal plate in FIG. 12 is used. Accordingly, if the press force is small, such a spring element is not deformed and therefore the knives 103 come into no contact with the resin-discharge surface over the entire circumferential contact areas, thereby occasionally causing the incomplete cutting to be provided. On the contrary, if the press force is increased to securely come into contact therewith over the entire contact area, the press force is greatly increased at areas at which knives and resin-discharge surface is in contact with each other in the initial state, so that the resin-discharge surface 102 in the die plate may be injured. This causes the abrasion of the knives 103 to be accelerated, and further the bending of the knives 103 due to the bending force applied thereto forces the root of the knives to come into contact with the die plate 101, so that a space occurs between the knives and the die plate at the end part of the knives. This also provides an incomplete cutting, a break in the knives and the other troubles.